380 PROCEEDINGS OF THE ACADEMY OP [1881. 



side truncate supporting the first interradial, and parallel with 

 the lower one. Owing to this construction, the basals have a 

 subquadrangular outline, and the lower angle of the first radials 

 almost touches the upper angle of the underbasals. 



Primary radials 3 X 5, of nearly equal size, the first pentagonal, 

 the second hexagonal, the third again pentagonal, and support- 

 ing two secondary radials (2X10). Tlie first plate larger 

 than the second, the latter axillary, but the sloping sides not of 

 equal width. The longer side, next to the middle of the ray, 

 supports an indefinite number of radials, and these extend into 

 free appendages ; while the other, shorter side, gives off laterally 

 the first arm. There are two of these appendages to each ray, 

 which at the base are connected by one or more interaxillary 

 plates, they are thick, puffy, cylindrical, three or four times as 

 long as the body, decreasing in width upwards. The plates which 

 constitute the outer or dorsal side of the appendages are short, 

 very wide, with parallel sutures, and from them, at certain 

 intervals — from every fourth or fifth plate, and from alternate 

 sides — the true arras arise. The latter are not given off strictly 

 laterally, as the separation from the main trunk actually begins 

 in the median portion of the two or three preceding plates of each 

 order, which show more or less deep oblique incisions. All arms 

 have nearly the same length, and hence do not reach the same 

 general height, those nearer the body are comparatively heavier. 

 The four or five proximal plates of the first arm are laterally con- 

 nected with the main trunks of the ray, the succeeding arms 

 become detached sooner, and the upper ones are free from their 

 base up. Each arm tapers to a sharp point, is composed of two 

 series of interlocking plates, with closely arranged, sword-like 

 pinnules. 



Interradial series composed of six to eight plates ; the first 

 large, heptagonal, supported upon the truncate upper side of the 

 basals, between the first radials and the lower sloping side of the 

 second, thus separating the entire radial series ; the second range 

 is composed of two somewhat smaller plates, the third of two or 

 three pieces, with one or two plates above. The posterior side is 

 but rarely distinct, it has exceptionally three pieces in the second 

 series. 



Vault scarcely rising above the limits of the calyx, slightly ele- 

 vated in the radial regions. It is constructed of an immense 



